Financial Instruments And Marketable Securities (Narrative) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010
Financial Instruments And Marketable Securities [Line Items]
Dollar value of transfers between levels	$ 0	$ 0
Government And Agency Securities [Member] \| Fair Value, Inputs, Level 1 [Member]
Financial Instruments And Marketable Securities [Line Items]
Debt instrument maturity date in months	12

The dollar amount of transfers between the three levels of fair value hierarchy.

No definition available.

Name:	fast_MarketableSecurityLevelTransfers
Namespace Prefix:	fast_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration